Process for making high-tenacity, low elongation industrial yarn



p 3, 1968 J. D. BOONE :TAL 3,400,194.

PROCESS FOR MAKING HIGH-TENACITY, LOW ELONGATIQN INDUSTRIAL YARN Filed Nov. 4, 1953 UNDRAWN YARN SUPPLY DRIVEN NDT FEED ROLLS 70-IDD0 FIRST STAGE DRIVEN HDT DRAW ROLL l20-l6D'D SECOND STAGE DRIVEN HDT DRAN RDLLS lDD-IZS'D INTERLADING JET WINDUP TNVENTORS JOHN DOUGLAS BOONE L VERNON KNIGHT BYWZIflZwA-Mm,

ATTORNEY United States Patent 3,400,194 PROCESS FOR MAKING HlGH-TENACITY, LOW ELONGATION INDUSTRIAL YARN John Douglas Boone, Donelson, Tenn., and Daniel Vernon Knight, Seaford, Del., assignors to E. I. du Pont de Ncmours and Company, Wilmington, Del., :1 corporation of Delaware Filed Nov. 4, 1963, Ser. No. 321,260 Claims. (Cl. 264-290) ABSTRACT OF THE DISCLOSURE A high-speed two-stage process for drawing polyester filaments using a feed roll (70-100 C.), first draw roll (l-160 C.) and second draw roll (l00125 C.) consisting of drawing in the first stage to a ratio of about 4:1, in the second stage to a total ratio of 5.5:1 to 6.521 and winding up under tension sufiicient to prevent shrinkage which results in a high tenacity, low elongation product useful for rope and cordage.

This invention relates to multi-stage drawing in the manufacture of synthetic linear condensation polyester fibers. More particularly, it is concerned with a highspeed process for preparing strong, low-elongation yarns of polyester fibers useful in the manufacture of ropes and cordage.

Synthetic linear polyester fibers, such as those prepared from polyethylene terephthalate, are Well-known articles of commerce, exhibiting outstanding performance in areas requiring strength, modulus, abrasion resistance, and resistance to degradation upon exposure to light, heat, and corrosive chemicals. These properties are particularly valuable when the fibers are formed into ropes, hawsers, and cordage. But in the field of marine usage, particularly in-harbor towing, where maximum strength combined with minimum extensibility is required, an economical process has not been available for preparing polyester fibers with the necessary combination of high tenacity and low extensibility.

Many manufacturing process variations are known for preparing fibers of synthetic linear condensation polyesters, but perhaps the best-known process for preparing high-strength yarns for industrial uses, tire yarns, ropes and the like, is the two-stage hot-draw process of Pace described in US Patent No. 2,556,295. An application of the Pace procedure involves drawing yarn at a draw ratio of about 4:1 (3.5:1 to 4.521) at a temperature of 60 to 100 C. and then further drawing the yarn at a temperature of 160 to 200 C. to a total draw ratio in the range of 5:1 to 6:1, e.g., with second-stage draw roll or rolls rotating at a peripheral speed of 5 to 6 times that of the feed roll or IOlls in a continuous drawing process.

However, Pace teaches that increases in tenacity, accompanied -by decreases in elongation, are obtained by increasing the draw ratio, and that maximum tenacities are obtained with total draw ratios in excess of 6:1, preferably at 66:1. The Pace procedure has been found unsatisfactory for high speed production of yarns having maximum tenacities in combination with minimum extensibilities, i.e., having a break elongation below about 10%. When attempting to operate at high speeds in this manner to produce yarns having extensibilities of about 10% or lower, the higher draw ratios are accompanied by an increase in broken filaments and threadline breaks, with a resulting decrease in yarn quality and productivity.

The primary concern of the present invention is to provide a practical high-speed drawing process capable of producing synthetic polyester yarns possessing high tenacity in combination with low extensibility. It is fur- 3,400,194 Patented Sept. 3, 1968 ther desired that this process operate smoothly at high speed to produce low-extensibility yarns without the occurrence of excessive broken filaments or poor package formation.

In accordance with the present invention, it has been found that, in the continuous two-stage hot-draw process for drawing yarns of synthetic linear condensation polyester by means of heated feed roll or rolls followed by first-stage and second-stage draw rolls, undrawn yarn can be drawn at high speed to impart high strength in combination with low extensibility by drawing the yarn at a temperature between 60 and 110 C. in the first stage, additionally drawing the yarn at a temperature between 120 and 160 C. in the second stage to a total draw ratio of 5.5 :1 to 6.5 :1, then partially cooling the yarn while still under the drawing tension to a temperature which is between 10 and 35 C. below the maximum drawing temperature, and passing the yarn to a windup.

The initial undrawn yarn should have a birefringance of less than 0.0030. The yarn is preferably heated to the first-stage drawing temperature during passage around a feed roll heated to between 70 and 100 C., is heated to the second-stage drawing temperature during passage around a draw roll heated to between 120 and 160 C., is partially cooled under drawing tension during passage around a second-stage draw roll heated to between 100 and 125 C., and is thereafter maintained under a tension of 0.2 to 0.5 gram per denier until and while the yarn is being wound up to form a package. The above process can be operated at high speed, without difiiculty with broken filaments or threadline breaks or sloughing of yarn from the windup package, to produce yarn having tenacities greater than 8 grams per denier at break elongations of 8% to 10%. The process operates smoothly with peripheral feed roll speeds of 300 to 700 yards per minute or windup speeds of 2000 to 4000 yards per minute Successful operation at such great speed is highly unexpected in view of the prior art disclosures.

The drawing is a schematic illustration of the process of this invention showing undrawn yarn being drawn by means of heated driven rolls, the drawn yarn then passing through an interlacing jet and being wound up. Ohviously, a plurality of driven rolls can be used in place of any of the rolls shown, and the terms feed roll, firststage draw roll and second-stage draw roll, as used herein, are intended to comprehend one or more rolls at each of these locations.

In carrying out a preferred embodiment of the process, undrawn polyethylene terephthalate yarn is passed to and around a feed roll rotating with a surface speed in the range 300 to 700 yards per minute and heated to a temperature between and C. The heated yarn is then passed to and around the first-stage draw roll, which is rotating at a surface speed about 4 times that of the feed roll. The first-stage draw roll is heated to a temperature between and 160 C. The hot yarn next passes to and around the second-stage draw roll, which is rotating at a surface speed about 6 times that of the feed roll and is heated to a temperature between 100" and C. which is at a temperature between 10 and 35 C. below that of the first-stage draw roll. The fully drawn yarn is then passed through an interlacing jet as described by Bunting et al. in US. Patent No. 2,985,995, and is finally passed to a windup operating at a speed between 3% and 10% slower than that of the second-stage draw roll.

The above embodiment is particularly suitable for producing heavy denier yarns. For light deniers, such as yarns of 100 to 500 denier after drawing, the feed roll is preferably heated to a temperature between 70 and 80 C.

Surprisingly, operation of this drawing process with the second-stage draw roll heated to the specified tem' perature provides very smooth performance. Attempts to modify the process by utilizing an unheated (room temperature) roll as the second-stage draw roll results in erratic threadline tensions and sloughing of yarn from the windup package. On the other hand, as illustrated in the examples, there is an unexpected increase in elongation when second-stage draw roll temperatures higher than 125 C. are used. At 145 to 165 C. yarn extensibilities several percentage points higher are ob tained than with the process of this invention, other conditions being equal. For yarns with extensibilities in the neighborhood of 8% to a change of even /2 percentage point is considered highly significant since extensibility is magnified by a factor of 3 or more in the transition from yarn to ropes and hawsers.

The term extensibility as used herein refers to elongation-to-break. High-strength polyester yarns may be economically prepared by the process of this invention with extensibilities in the range of 8% to 10%. For hawsers used in in-harbor towing, these low extensibilities are necessary to afford good control of harbor craft. It is noteworthy that synthetic fibers which inherently possess high extensibilities, such as nylon, cannot be made into satisfactory hawsers for this use.

The expression synthetic linear condensation polyester used herein refers to those polymers consisting of chain segments composed of carbon and hydrogen connected by linking units having the formula Such polyesters include those described by Whinfield and Dickson in U.S. 2,465,319, of which ethylene terephthalate polymers, which may also comprise minor amounts of other polyester-forming components, are the best known commercial examples. The polyester should have an intrinsic viscosity of at least about 0.6. Intrinsic viscosity may be measured as disclosed by Pace in U.S. Patent No. 2,556,295.

The term undrawn yarn refers to freshly spun yarn which has not been stretched. It is preferred that the undrawn yarn possess as little pre-orientation as possible and, in any case, its optical birefringence should be less than about 0.0030.

The high speed at which the present process can be operated is an important advantage over the lower, more conventional drawing speeds. By high speed is meant windup speeds in the range 2,000 to 4,000 y.p.m. Speeds in this range greatly magnify process and equipment problems.

The following examples are presented to more fully illustrate the invention and are not intended to limit it in any way.

EXAMPLE I (a) Polyethylene terephthalate having an intrinsic viscosity of 0.68 is melt spun at a temperature of 300 C. using a 250-hole spinneret plate. The extruded filaments are quenched in cross-flow air and then brought together into a yarn bundle which is passed around a driven feed roll and separator roll, operating at a surface speed of 512 y.p.m. The feed roll is heated to a temperautre of 85 C. Eight wraps are made around the pair of feed rolls to give a total wrap length of 5.8 yards. The yarn is then passed to and around the firststage draw roll, with its accompanying separator roll, which is driven at a surface speed of 2,050 yards per minute and is heated to a temperature of 135 C. Nine wraps are made around the first draw roll pair giving a total wrap length of 7 yards. The yarn is next passed to and around a pair of driven second-stage draw rolls operating at a surface speed of 3,040 y.p.m. and heated to the temperature noted in Table 1. Nine Wraps are made around the second-stage draw roll pair, giving a total wrap length of 9.5 yards. The total draw ratio at TABLE 1 Sample No. 2 draw Break elonga- Tenacity,

roll temp. tion, percent g.p.d.

A (control) 165 11. 4 8. 5 13 (control) 145 11.0 8.6 0 (test) 9. 8 8. 7 D (test) 105 9. 4 8. 5

The data in the table clearly show the marked reduction in break elongation achieved by adjusting the secondstage draw roll temperature in accordance with this invention.

(b) For comparison purposes, an attempt is made to operate the above process with the second-stage draw roll at room temperature about 25 C. Erratic threadline tensions are encountered with the yarn sloughing olf the windup package before a full package can be obtained. The process is considered inoperable.

(c) For comparison purposes, an attempt is made to produce yarn of low break elongation by using higher draw ratios in combination with heat setting. The second-stage draw roll temperature is maintained at least as high as the maximum draw temperatures as taught by Leben and Little in British Patent 603,840. Other conditions are as in (a) above. The values for break elongation and tenacity of the yarns produced at several draw ratios are recorded in Table 2 below. The data in the table illustrate the difiiculty in achieving break elongations of 10% or below with increased draw ratio alone. The yarn breaks experienced at a draw ratio of 6.30:1 indicate the closeness of the process to the ragged edge of inoperability at these high draw ratios.

TABLE 2 Sample Draw No. 2 draw Break elonga- Tenacity,

ratio roll temp. tion, percent g.p. 1.

(Excessive threadline breaks) EXAMPLE II Drawn yarn samples A and D from Example I(a) are each twisted and plied into a standard marine rope having a 4 /2" circumference. Tensile tests made on the rope samples give the results in Table 3. The magnification of elongation differences between the two samples in going from yarn to rope is obvious from an inspection of the data in the table.

The general procedure of Example I is repeated with the exception that a 100-hole spinneret is used and the polymer throughput is adjusted to give a 440-denier (49 tex) drawn yarn. The feed roll is maintained at 75 C., the first-stage draw roll is maintained at 135 C. and the second-stage dnaw roll is maintained at a temperature of 120 C. The over-all draw ratio adjusted to 6.0. The yarn produced has a break elongation of 9.8% and a tenacity of 8.4 g.p.d.

The same procedure when using a second-stage draw roll temperature of 160 C. gives a yarn with a break elongation of 11.2% and a tenacity of 8.3 g.p.d.

EXAMPLE IV This example illustrates the preparation of a 220-denier yarn.

The procedure of Example III is repeated, using a 50- hole spinneret and adjusting the polymer throughput to give a 220-denier (24.5 tex) yarn. The roll temperatures and draw ratio are the same as in Example III. The drawn yarn has a break elongation of 8.15% and a tenacity Olf 7.8 g.p.d.

Although the invention has been illustrated above with specific reference to yarns made from polyethylene terephthalate, it will be apparent to those skilled in the art that the invention may be applied to any synthetic linear condensation polyester capable of being spun and drawn to high tenacity yanns by the two-stage hot drawing process of Pace. The simplicity of the invention makes it immediately applicable to high-speed pnocesses for manufacturing polyester yarns, especially those processes in which the yarn drawing step is coupled directly to the melt spinning step. The benefits accrue to any area in which a yarn of very low extensibility is desirable, particularly when used as ropes, hawsers, and cordage.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

We claim:

1. The continuous two-stage hot-draw process for highspeed drawing of synthetic linear condensation polyester filaments to produce yarn having tenacities greater than 8 grams per denier at break elongations of 8% to 10% which comprises feeding undrawn y-arn filaments, having a birefringence of less than 0.0030, around a feed roll rotating at a peripheral speed within the range of 300 to 700 yards per minute and having a temperature between 70 and 100 C. to heat the yarn filaments; passing the heated yarn filaments around a first-stage draw roll having a temperature between 120 and 160 C. and rotating at a peripheral speed about 4 times that of the feed roll to draw the yarn filaments; passing the yarn filaments without further heating around a second-stage dr-aw roll rotating at a higher peripheral speed to further draw the yarn filaments to a total draw ratio between :1 and :1, the second-stage draw roll having a temperature between 100 and 125 C. to partially cool the yarn filaments under drawing tension; and then winding up the drawn filaments as yarn under a tension of 0.2 to 0.5 gram per denier at a speed of 2000 to 4000 yards per minute.

2. The process as defined in claim 1 wherein the second-stage draw roll is rotating at a peripheral speed about 6 times that of the feed roll and the yarn is wound up at a speed between 3% and 10% slower than that of the second-stage draw roll.

3. The process as defined in claim 2 wherein a yarn of 100 to 500 denier is fed to the feed roll and the feed roll has a temperature between and C.

4. The process as defined in claim 2 wherein a yarn filament bundle of greater than 500 denier is fed to the feed roll and the feed roll has a temperature between 80 and C.

5. The process as defined in claim 2 which includes the step of interlacing the yarn prior to winding up the yarn.

References Cited UNITED STATES PATENTS 2,615,784 10/1952 McClellan 264-290 3,216,187 11/1965 Chantry et a1. 264-210 2,556,295 6/1951 Pace 264290 2,611,923 9/1952 Hume 264290 FOREIGN PATENTS 628,863 10/ 1961 Canada.

10/ 1961 Canada.

OTHER REFERENCES JAMES A. SEIDLECK, Primary Examiner.

HERBERT MINTZ, Assistant Examiner, 

